The Acid phosphatase-1 gene region in the Drosophila species of the subobscura cluster

The acid phosphatase-1 (Acph-1) gene region was sequenced in three species of Drosophila: D. subobscura, D. madeirensis and D. guanche. These three cl osely related species, which are included in the obscura group, form the su bobscura cluster. The different functional regions of the gene were identif ied by similarity with the sequence of D. melanogaster. The structure of Ac ph-1 is conserved in the four species. Average divergence at synonymous and nonsynonymous sites between D, melanogaster and the species of the subobsc ura cluster is K-s = 1.1354 and K-a = 0.1743, respectively. The rather high K-a value confirms that ACPH-1 is a rapidly evolving enzyme in Drosophila, as previously suggested by immunological studies. Amino acid replacements are not randomly distributed along the gene. In fact, an excess of replacem ents is detected in exon I, indicating that the signal peptide encoded by t his exon evolves even faster than the rest of the protein. Divergence at th e Acph-1 gene region is further evidence that D. madeirensis and D. subobsc ura are more closely related than D, guanche is to any of them. In addition , both silent divergence in noncoding regions and synonymous divergence in the coding region indicate that the split of the D. guanche lineage is abou t twice as old as the split of the lineages leading to D. madeirensis and D . subobscura. These phylogenetic relationships are, however, not supported by divergence at nonsynonymous sites since the lowest K-a estimate is betwe en D. guanche and D. subobscura.